If there's one thing I could guarantee that you hate it is the idea of being surprised by a spider while you're driving.
Snakes in cars are always a possibility too, but spiders are far more common.
Anyway, I believe the reason that foreigners have a perception about Australia being full of dangerous creatures, whereas those of us who live here are not scared of that fact on a constant basis, is - and this is the clever bit - we expect to find dangerous creatures from time to time. They're not all that big of a surprise to us, usually. And we know roughly when and where to expect each type.
Therefore, the first thing I'd suggest is to think of the car the same as you should your bed or clothes or shoes and actually expect spiders or another creepy crawly to be hiding somewhere in there, look for them, and be pleased when you don't find one.
Treat the car the same as you would a bed or a shoe by assuming there are spiders in it and dealing with them before going in
The next thing I'd suggest is get more familiar with the species in your area. If you can identify it in milliseconds you'll be more able to identify the threat level too, and then you'll be able to avoid some even more dangerous action like swerving, braking or otherwise panicking before you can find a safe place away from other traffic to stop.
Another advantage of being able to identify them quickly is each species of spider will have a different likelihood of actually emerging suddenly as well. Some will just stay put and ride out the simulated storm. Others will respond to (or will simply get disturbed by) the bumps and vibrations and may emerge in your view because of them.
The other thing about familiarising yourself with the various species found in your patch is it will give you an indication of where to look as well. Spiders that make webs will find crevices like wheel arches and door jambs and gaps around mirrors. Basically anywhere they're likely to catch a six-legged flying feed. The redback spider in particular loves wheels and wheel arches for some reason. Huntsmans or garden wolf spiders will find places they can hide from predators while they're not out (usually at night) doing their own hunting. Again think door jambs, but also inside like behind sun visors, under seats and under dashboards.
Having also safely assumed that spiders will want to take refuge in some crevice of your parked vehicle, there are a few options you can deploy to discourage them.
Where you park may have an influence, like in garages and near gardens (where they play an important role controlling pests). But you want the vehicle safe and sheltered, so parking elsewhere isn't terribly attractive.
There are natural remedies that work, just as they do for your house, but some damage your paint so be careful what you treat, or maybe treat around the car. Diluted white vinegar is a good cleaner, but you can't leave it on. Peppermint oil and other essential oils can damage paint too. Same goes for lemon peels and scents based on them.
Insect surface sprays work, but also need to be tested to ensure they won't affect your paint, plastic, rubber or trim over time.
A regular wash and vacuum can be helpful (and then your chosen treatment after), if you are properly thorough and remember all the places they might be hiding. Apart from clearing webs and flushing the spiders out, it also gets rid of things that may attract insects, which in turn attract spiders.
Ensuring everything is shut properly, the windows are fully closed, and the rubber weather seals are all in good condition, will make it harder for spiders to enter (but never impossible, and they can sneak in from the door jamb when you open the door).
So it's like anything else I guess. Be aware, be prepared, and be vigilant, and you won't be as likely to get an unwanted eight-legged surprise while you're driving.